The present invention relates to digital processing of radar video data and more particularly to a system and technique for providing near real-time video compression and read-while-write capability of the data to improve visual presentation thereof.
Modern radar displays commonly employ a cathode ray tube (CRT) device in conjunction with computer-generated graphic information (graphics) to enhance the radar video presentation. To effectively utilize such radar displays, it is desirable to maximize the time available for the graphics presentation and consequently, the graphics loading capability of the display, without the loss of real-time video. Generally, the graphics time available is inversely proportional to the selected radar range for displaying real-time video, assuming a constant pulse repetition frequency (PRF) for the radar. Therefore, for a certain refresh period during which character writings of the radar video must be rewritten on the CRT to avoid refresh degradation (an observable flicker), the maximum time generally available for graphics occurs when the minimum range is displayed in real time. For greater displayed ranges, the graphics time and loading capability decrease, and refresh degradation of the graphics presentation occurs as a result of rapid graphics overloads.
While various processing techniques have been developed for increasing the graphics time and loading capabilities of existing radar display systems, none have been entirely satisfactory throughout the selected display range scales without losing real-time video. One such technique used to complete the graphics presentation of a CRT display without flickering periodically ignores real-time video scan periods as the display range increases and the graphics load approaches the maximum capacity within the refresh period of the display. Furthermore, existing radar display systems have had to vary the writing rates of a scan trace of real-time video across the CRT as a function of the selected display range, and as a result, have been required to employ complicated compensating circuitry for readjusting the grid drive of the CRT to maintain a constant background brightness.